Methods and machines suitable to count piles of sheets arranged in a stack form for example securities such as banknotes, are known in the art. One of the known devices is disclosed in EP patent application No 0 737 936.
This patent application, the content of which is enclosed by reference in the present application, discloses a counting disk of a sheet counter for sheets arranged in stack form, in particular notes of value, said rotatable counting disk having circumferential sections which are arranged at regular intervals on the border of said disk and have protrusions projecting in the direction of rotation of the disk, and each circumferential section having a counting opening, a pneumatic counting pulse being triggered when said opening is covered by a sheet, having a suction hollow, whose width and depth increase in the direction counter to the direction of rotation of the disk, and having a group of suction openings which are located one behind the other, are arranged in said suction hollow and can be connected intermittently, via suction ducts, to a negative-pressure source, such that, during operation, the abovementioned circumferential sections leaf through all the sheet corners of a sheet stack one after the other, separate these from one another in the process, under the action of suction and deformation, and cause each sheet to be counted. In the known device, the abovementioned suction openings are located in the center of the suction hollow, the sections, opening into the suction openings, of the suction ducts are directed essentially perpendicularly with respect to the disk plane and with respect to the base of the suction hollow, and the suction force acts centrally on the suction hollow and perpendicularly with respect to the base of the suction hollow.
Normally, these counting disks are used on one or two corners of the stack of sheets, thus giving one single counting value or two counting values, e.g. one counting value for each corner. To increase the number of counting values, it is possible to rotate the stack of sheets by 180° and carry out another counting operation on the two other corners of the stack. With such a system, it is hence only possible to obtain a maximum of four counting values for a given stack, in at least two counting operations.
Other known prior art methods and devices include Swiss patent CH 422 834, PCT international application No WO95/00926, GB patents No 931,463, No1,139,292 and No744,957, Russian publications No 859204 and No2007759 C1, and also U.S. Pat. Nos. 3,904,189 and 3,953,022.
All these prior art publications are based on mechanical systems that contact and count the sheets. Usually, as described in EP 0 737 936, the disk travels across the stapled banknotes or securities and at each passage of a successive sheet or banknote, the system will increment a counting value and finally, the end counting value will give the number of sheets/substrate present in the pile. One drawback in such mechanical counting is the fact that the disk, or equivalent means, may damage the substrate being counted. Further, the system is rather slow (more than 8 seconds for 500 sheets of substrate) and noisy.
Another apparatus and process for counting sheets in a pack is disclosed in EP patent application 0 743 616, the content of which is enclosed by reference in the present application. In this patent application, a linear CCD array is used to create a signal representing a high-resolution one-dimensional line scan of the height of a pack that is positioned between stiffening boards used to increase the rigidity of the pack. Optionally, a compression of the pack is carried out by pressure plate and a piston/clamping assembly before the image is made. The signal corresponding to the image is digitised, stored and then processed by different means (Gaussian filtering, one-dimensional Fast Fourrier Digital Transform etc.). In one specific embodiment, a static two-dimensional CCD array is used to provide a two-dimensional signal and additional signal processing is carried out to translate the signal into a one-dimensional signal along the height of the pack being counted. The two-dimensional CCD array includes rows and columns which are positioned to the pack such that the rows of the array align approximately with the sheets to be counted in the pack. Additional signal processing then averages the values within each row, or samples one column to produce a one-dimensional signal. However, according to this publication, it is preferred to use a linear CCD array camera also for costs reasons and for speed of processing reasons.